This invention relates to a method and apparatus for centrifugal separation of a dispersed phase from a continuous liquid phase. "Dispersed phase" in this specification means a dispersed solid or liquid phase. More particularly, though not exclusively, this invention relates to the removal of wax particles from a hydrocarbon oil mixture boiling in the lubricating oil range. The term "wax particles" herein means wax in any particulate form and includes wax crystals. Furthermore, throughout this specification, it is to be understood that "hydrocarbon oil mixture" and "oil mixture" both mean a hydrocarbon oil mixture boiling in the lubricating oil range.
The problems of wax in lubricating oil are very well known in the art. In the distillation of crude oil, a proportion of wax is present in cuts taken in the lubricating oil range. Some of the wax remains dissolved in the oil whereas other fractions form a haze as the oil fraction ages at ambient temperatures or below. Wax in itself is in fact a good lubricant but under comparatively low temperatures such as engine cold start conditions, its presence causes the oil to be thick and viscous and as a result the engine may be hard to turn over at sufficient speed during starting. Typically, a minimum of about 0.1% by volume of wax will cause some lubricating oils to look hazy. Therefore, the existence of haze caused by the presence of wax crystals or particles detrimentally affects the performance of lubricating oils. It is of paramount practical importance to devise techniques for removing wax haze from lubricating oil in a relatively inexpensive, simple and effective manner, which techniques are also capable of implementation on an industrial scale. It is also of importance to separate dispersed phases from continuous liquid phases, generally.